1. Field of the Invention
The present invention generally relates to diverting sheets of a printable material, such as signatures severed from a web in, for example, a rotary offset printing press.
2. State of the Art
Devices for diverting signatures are known. For example, signature diverters are used to divert successive signatures in an incoming signature stream into two or more output streams. Signature diverters are used when, for example, downstream processing systems cannot operate at the speed of the incoming signature stream. In this case, two parallel downstream processing units can be configured to receive alternate ones of the incoming signatures, such that they can be operated at half the speed of the incoming signature stream.
Diverters are also used where successive signatures in an incoming signature stream contain alternating images. This occurs when, for example, the printing of a web of material is performed with a print cylinder that prints two different images on signatures during each rotation (that is, two around print cylinders). In this case, when the signatures are severed from the web, every other signature contains one of two different images, in alternating fashion. It is often desired to shift every other one of the signatures output from the print cylinder into one of two downstream signature streams in alternating fashion. That is, where the print cylinder imparts an "A" image to one signature, and a "B" image to a succeeding image, it is often desirable to divert the severed signatures into a stream of only A signatures and into a separate stream of only B signatures.
Conventional signature diverters have been implemented using bump turns. A conventional bump turn involves transporting a signature into a wall to change a velocity vector of the signature (i.e., speed and direction of the signature) into a new velocity vector instantaneously. However, in actuality, frictional forces prevent an instantaneous transition of the signature from an original velocity vector to a new velocity vector, such that conventional bump turns suffer significant disadvantages. Among the disadvantages are their unreliability in initiating a new velocity vector, the potential damage they cause to the signatures, and the potential jamming of the press which can result. In addition, conventional bump turns cannot be used to separate "A" signatures from "B" signatures. Rather, a separate downstream splitter device must be used to separate the signature stream into multiple substreams.
Accordingly, it would be desirable to provide a method and apparatus for diverting and separating signatures in a cost effective, efficient manner which does not require the use of independent diverter and stream splitter devices, and which does not result in potential damage to the signatures or jamming of the press.